Tip clearance in a gas turbine varies depending on the expansion and contraction of rotation-side structural members and stationary-side structural members due to the difference between the temperature during start-up and that during rated operation, and by the centrifugal extension thereof due to the rotation. That is, the variation in the tip clearance is influenced by the temperature at the outlet of a compressor and the temperature of combustion gas, making the clearance of first-stage turbine rotor blades particularly tight.
In a conventional structure, when there is no temperature adjusting means (for example, a steam path) on the stationary side of a turbine unit, the amount of thermal expansion of a blade ring varies depending on the temperature at the outlet of the compressor. Therefore, when the tip clearance during the above-mentioned rated operation is to be minimized, the initial clearance has to be set with no allowance for contact.
Furthermore, in order to deal with the above-mentioned tip clearance, active clearance control (hereinafter referred to as “ACC”) for ensuring the tip clearance required during start-up and for achieving the minimum tip clearance during rated operation is performed.
In this ACC, clearance control using steam is performed to increase or decrease the tip clearance of the first-stage turbine rotor blades during operation. More specifically, the clearance is controlled through control of the thermal expansion by heating the blade ring with steam introduced from outside the gas turbine during start-up of the gas turbine and by cooling the blade ring during load operation.
In order to perform the above-mentioned clearance control, an ACC blade ring has, therein, a steam path for heating and cooling. Thus, even if a first-stage blade ring is exposed to a space at the outlet of the compressor, the amount of expansion of the blade ring that may affect the tip clearance is determined by the relationship between the discharge temperature of the compressor and the steam temperature, whereby the amount of thermal expansion of the blade ring can be adjusted. Accordingly, because the tip clearance is increased by heating with steam during start-up and is reduced by cooling with relatively low-temperature steam during load operation, the tip clearance can be adjusted according to the operating conditions (for example, see Patent Citation 1).
Furthermore, a gas turbine is disclosed in which cooling means that cools air for cooling turbine stator blades is provided, and the air cooled by this cooling means is supplied to the turbine stator blades, whereby the amount of discharged air introduced from the air compressor as the air for cooling the turbine stator blades and the amount of air bled from an interstage are reduced to improve the thermal efficiency (for example, see Patent Citation 2).
Patent Citation 1:
The Publication of Japanese Patent No. 3825279
Patent Citation 2:
Japanese Unexamined Patent Application, Publication No. Hei-7-54669